This invention relates to resist materials and, in particular, to improved positive-working resist materials capable of forming on a substrate either a positive resist pattern or a negative resist pattern, and their use in the formation of a negative resist pattern on the substrate.
A variety of resist materials which are useful for forming a desired pattern on a substrate in the production of semiconductor devices are well known in the art. These resist materials are usually classified into two types, namely, negative-type resist materials, which are adapted to form a negative image on a substrate, and positive-type resist materials, which are adapted to form a positive image on a substrate. An unexposed portion of the negative resist material is dissolved in a developer and, as a result of this, a negative image is formed, while an exposed portion of the positive resist material is dissolved in a developer and, as a result of this, a positive image is formed. Representative examples of the negative resist materials include polyvinyl cinnamate photoresists, cyclized rubber photoresists and the like, and representative examples of the positive resist materials include napthoquinonediazide photoresists, benzoquinonediazide photo-resists and the like.
The negative and positive resist materials are used selectively depending upon such factors as the desired image, the particular developer utilized, in particular pattern-forming step used, the particular etching step utilized and the like. However, the selective use of these two materials is technically troublesome and may frequently cause many working errors or mistakes in the fabrication of integrated circuits. Furthermore, in general, the positive resist materials can provide images having an excellent definition, which is higher than that of the images formed through the use of the negative resist materials. Thus, for the purpose of attaining a simple and correct fabrication of integrated circuits at a low cost, it is desired to provide an improved resist material which is useful to optionally form on the substrate either a positive resist pattern or a negative resist pattern. Furthermore, the formed negative resist pattern should have a relatively higher definition. If a higher definition is attained in the resist pattern, the integration of the resulting integrated circuits is increased.
In Japanese Patent Application No. 51-66664, filed on June 9, 1976 (now Patent Laid-open Gazette No. 52-6528), there is disclosed a method of forming a resist layer with a negative pattern on a substrate by using a positive resist containing 1-hydroxyethyl-2-alkylimidazoline. This method comprises the steps of: preparing a substrate having coated thereon a positive-working resist layer containing 1-hydroxyethyl-2-alkylimidazoline, exposing said resist layer to a pattern of radiation, heating said resist layer to a temperature sufficient to insolubilize the exposed area of said layer in a developing solution which will be used in a subsequent step, subjecting said resist layer to a blanket exposure and developing said resist layer with said developing solution. This method is considered to be similar to that of the present invention with regard to the formation of a negative pattern on the substrate by using the positive resist, but cannot fully solve the problems set forth above.